Ecological interactions and genomic innovation fueled the evolution of ray-finned fish endothermy

Endothermy has independently evolved in several vertebrate lineages but
remains rare among fishes. Using an integrated approach combining
phylogenomic and ecomorphological data for 1,051 ray-finned fishes, a
time-dependent evolutionary model, and comparative genomic analyses of 205
marine vertebrates, we show that ecological interactions with modern
cetaceans coincided with the evolution of endothermy in ray-finned fishes
during the Eocene–Miocene. This result is supported by evidence of
temporal and geographical overlap between cetaceans and endothermic fish
lineages in the fossil record, as well as correlations between cetacean
diversification and the origin of endothermy in fishes. Phylogenetic
comparative analyses identified correlations between endothermy, large
body sizes, and specialized swimming modes while challenging diet
specialization and depth range expansion hypotheses. Comparative genomic
analyses identified several genes under selection in endothermic lineages,
including carnmt1 (involved in fatty acid metabolism) and dcaf6
(associated with development). Our findings advance the understanding of
how ecological interactions and genomic factors shape key adaptations.